Pyrolysis of tris(2-carboxyethyl)-isocyanurate

ABSTRACT

Tris(2-carboxyethyl)isocyanurate and esters, amides, anhydrides and acid halides thereof undergo pyrolysis to afford cyanuric acid and acrylic acid or the corresponding ester, amide, anhydride or acid halide thereof. The process provides an in situ source of acrylate derivatives.

United States Patent 1 3,697,584

Little [451 Oct. 10, 1972 [54] PYROLYSIS OF TRIS(2- [58] Field of Search..260/486 R, 486 D, 153, 526 N,

CARBOXYETHYL) -ISOCYANURATE 260/561 N, 544 Y, 546

[72] Inventor: Edwin D. Little, Convent Station, Primary ExaminerLorraine Aweinberger Assistant ExaminerR. S. Weissberg [73] Assignee:Allied Chemical Corporation, New Attorney-Michael 131052 York, NY. [57]ABS CT 22 Filed: Dec. 16, 1969 r1s -car x e 1800 anurae an e e 1 T (2 b0y thyl) y t d st rs amdes PP 885,649 anhydrides and acid halides thereofundergo pyrolysis to afford cyanuric acid and acrylic acid or thecording ester, amide, anhydride or acid halide 52 US. ca. .....260/486R, 260/248 cs, 260/486 1), The Y process provides an in sltu source of260/526 N, 260/544 Y, 260/546, acrylate derivatives.

[51] Int. Cl. ..C07c 57/04, C07c 69/54 11 Claims, No Drawings PYROLYSISOF TRIS(2-CARBOXYETHYL) ISOCYANURATE BACKGROUND OF THE INVENTION Thisinvention relates to a method of preparing acrylic acid and derivativesthereof, and in particular, relates to a method of preparation ofacrylates from tris(Z-carboxyethyl) isocyanurate and derivativesthereof.

Derivatives of isocyanuric acid are known to react in a variety of waysunder pyrolysis conditions, depending upon the substituents pendant fromthe triazine ring. For example, US. Pat. No. 3,l08,l l discloses thatthe tris(Z-hydroxyethyl) derivative undergoes detrimerization upon beingsubjected to elevated temperatures, especially at reduced pressure, toafford 2-oxazolidones. Alkyl esters of isocyanuric acid, on the otherhand, hydrolyze to carbon dioxide and primary amines upon being heatedin the presence of base. Karrer, Organic Chemistry (4th Eng. ed., 1950)p 237.

However, Smolin et al., s-Triazines (1959) p 406407,

indicates that variation of the base can give other products such astriethylbiuret, ethylene, ethanol, and triethylguanidine, and at page402 indicates that pyrolysis under acidic conditions affordsisocyanates. Carboxyl-substituted isocyanurates, on the other hand, arereported as being relatively stable under conditions which wouldpyrolyze other isocyanurate derivatives. For example, West German Pat.No. 812,312 of Aug. 27, 1951, discloses that the triethyl esters oftris(3-carboxypropyl)isocyanurate and tris(carboxymethyl)isocyanuratecan be subjected to temperatures as high as 250 C. at reduced pressurewithout decomposition. Similarly, US. Pat. No. 3,230,220 discloses thattris- (carboxymethyl)isocyanurate is substantially more sta ble onheating than is the ethyl homolog.

SUMMARY OF THE INVENTION It has now been found thattris(2-carboxyethyl)isocyanurate and derivatives thereof undergopyrolysis to afford acrylic acid and derivatives thereof. In addition tothe free carboxylic acid, derivatives oftris(2-carboxyethyl)isocyanurate which undergo analogous pyrolysisinclude esters, amides, acid halides and anhydrides thereof, therebyaffording a synthesis of various acrylate derivatives difficult toobtain otherwise.

The reaction is useful as a means of providing a high temperature insitu source of a variety of acrylic acid derivatives which are obtainedin surprisingly pure form. Cyanuric acid, or tautomeric isocyanuricacid, is a valuable by-product of the pyrolysis reaction, and can berecycled in the process. The formation of cyanuric acid is especiallyunexpected in that C-N scission in isocyanurate derivatives has neverbefore been observed to leave the triazine ring intact.

DETAILED DESCRIPTION OF THE INVENTION The instant invention involves apyrolysis reaction unique among isocyanurate derivatives whereby acrylicacid derivatives are obtained and the triazine ring is left intact. Theprocess proceeds according to the following sequence: 1

O o A o nodomcm- N-cHlcmtioH' A (BHzCHzCOH and includes within its scopethe various derivatives of carboxylic acids, e.g., esters, amides, acidhalides, acid anhydrides and other carboxylic acid derivatives. Thereaction also includes within its scope the pyrolysis of homologs 'oftris(2-carboxyethyl)isocyanurates, viz., tris(Z-carboxypropyl) andtris(2-carboxybutyl)isocyanurates and the ester, amide, acid halide andanhydride derivatives thereof. Thus, the reaction provides a method ofobtaining acrylic acid, alkyl acrylates, acrylamide, acryloyl chloride,various acrylic acid anhydrides, methacrylates, ethacrylates and otherrelated acrylic acid derivatives from the correspondingly substitutedcarboxyethyl isocyanurate. Hereinafter these derivatives arecollectively referred to as carboxylic acid derivatives of theisocyanurate or acrylic acids. The reaction is conducted underconditions sufficient to result in the desired pyrolysis of theisocyanurate reactant. The reaction requires elevated temperatures,although the required minimum temperatu'reto afford pyrolysis will varywith the particular isocyanurate selected as reactant, desired rate ofreaction, reaction pressure, and other considerations disclosedhereinafter. Typically, the reaction temperature for the instant processwill be at leastabout C., preferably within the range of about 250 C. Ofcourse,

temperatures outside this range may be found to be adequate in anyparticular reaction and the use of such temperatures is within the scopeof the instant invention. The most advantageous temperature to beemployed in any particular instance can be readily determined by simpleexperimentation.

Although it is possible to conduct the reaction at atmospheric pressureand even at super-atmospheric pressure, it is preferred, in the case ofnon-volatile acrylic acid products, to employ sub-atmospheric pressurewhen it is desired to separate the acrylate from the reaction mixture.Sub-atmospheric pressure also has the advantage of permitting lowerreaction temperatures and faster rate of reaction. In a more preferredembodiment, the reaction is conducted under vacuum distillationconditions, in which event the non-volatile acrylic acid product isobtained in pure form as distillate. Volatile acrylic products,on theother hand, such as the free acid and ethyl ester, can be easilyseparated at atmospheric pressure so that reduced pressures are not aspreferred in those instances. Also, when it is desired that the acrylateproduct be maintained in the reaction mixture, for example as a sourceof monomer for in situ polymerization, it will become advantageous tooperate at atmospheric or super-atmospheric pressure during thepyrolysis reaction, wherein the cyanu ric acid would sublime out of thereaction mass.

The pyrolysis reaction can be conducted either in the presence orabsence of solvent. Suitable solvents will be high boiling materialswhich are inert under pyrolysis conditions and tripropyl isocyanurate,Dowtherm and the like.

Reaction time will vary over a large range depending upon other reactionparameters and the extent to which 100 percent conversion is desired.Normally, the reaction must be conducted for at least 30 minutes toachieve an acceptable level of conversion, and it will be continued forup. to several hours or several days until the desired extent ofconversion is achieved. In this regard,it is noted. that pyrolysis ofthe isocyanurates involves substantially. more than mere melting of thereactant. I

When conducting the instant pyrolysis under conditions conducive toseparation of the acrylic acid product as it is formed, it will often befound that a quantity of cyanuric acid by-product sublimes over into thedistillate receiver. However, the cyanuric acid. is insoluble in theacrylic acid and it can be readily removed therefrom by filtration orother standard separation techniques.

Among the acrylic acid derivatives which are prepared by the instantprocess from the corresponding isocyanurate are the following:

Acrylic acid Methyl acrylate Ethyl acrylate Propyl acrylate i-Propylacrylate Amyl acrylate Z-Ethylhexylacrylate n-Octyl acrylate n-Decylacrylate Allyl acrylate Benzyl acrylate Cyclohexyl acrylate2-Chloropropyl acrylate 2,3-Dichloroprpyl acrylate Acrylamide N-Methylacrylamide N-Ethyl acrylamide N-Isopropylacrylamide N-BenzylacrylamideN,N-Dimethyl acrylamide N,N-Diethylacrylamide Acryloyl chloride Acryloylbromide Acrylic anhydride Acrylic acetic anhydride Acrylic propionicanhydride Acrylic benzoic anhydride Methacrylic acid Methylmethacrylate.

The reaction is especially advantageous for the preparation of acryloylchloride, acryloyl bromide,

include N-methylpyrrolidone,

chloroethyl acrylates and other acrylate derivatives difficult toprepare otherwise due to the unsaturation of the material.

The carboxyl-substituted isocyanurate reactants used in the instantinvention are readily prepared by procedures taught by the prior art, orby obviousmodifications to procedures taught by the prior art. Forexample, U.S. Pat. No. 3,235,553 disclosed the preparation oftris(Z-carboxyethyl)isocyanurate and alkyl triesters thereof. Furthermethods for the preparation of the esters are disclosed in U.S. Pat. No.3,332,945. Also, U.S. Pat. No. 3,432,500 discloses the preparation oftris(2-carboxamidoethyl)isocyanurate and various substituted amides. Byfurther reaction on these derivatives or modification of theseprocedures according to methods well known to those with ordinary skillin the art, other isocyanurate derivatives are readily available forpyrolysis to the desired acrylic acid compound. For example, thetriallyl ester of tris(2-carboxyethyl)isocyanurate can be prepared andchlorinated and then pyrolyzed to afford either the monochloro ordichloropropyl acrylate. Additionally the tris(2-carboxyethyl)compoundcan be reacted with any of a variety of other carboxylic acids to affordan appropriate anhydride from which an acrylic acid anhydride can beprepared.

The following examples are provided to illustrate the instant inventionmore fully. They are provided for illustrative purposes only and are notto be construed as limiting the invention, which is defined in theappended claims. Variations and modifications in the procedures of theexamples may be made by those with skill in the art without departingfrom the scope of the invention.

EXAMPLE 1 Tris(Z-carboxyethyl)isocyanurate (17 g.) was placed in avacuum distillation apparatus and heated at reduced. pressure to 200 C.Heating was continued until 4 g. of acrylic acid was collected asdistillate in a cold trap (71.5 percent yield on 53 percent conversion).Solid cyanuric acid, formed in the distillate by sublimation, wasremoved by filtration.

The pyrolysis reaction was also run with 0.1 g. of sodium hydroxideadded to the reaction mixture with similar results.

EXAMPLE 2 Tris(Z-carbethoxyethyl)isocyanurate (60 g.) was heated tol-200 C. in a distillation apparatus at atmospheric pressure until 23 g.of ethyl acrylate was collected as distillate (96 percent yield on 50percent conversion). Continued heating of-the distillation vesselafforded increased pyrolysis of the isocyanurate.

EXAMPLE 3 The octyl triester of tris(2-carboxyethyl)isocyanurate wasprepared by heating octyl alcohol and the isocyanurate in the presenceof 5 weight percent toluene until the theoretical amount of water hadbeen removed. After removal of the toluene, the octyl triester (m.p.24-26 C.) was then pyrolyzed according to the procedure of Example 1 toafford octyl acrylate and cyanuric acid.

EXAMPLE 4 The procedure of Example I ,is repeated using the followingisocyanurates to afford cyanuric acid and the corresponding derivativeof acrylic acid:

Tris(2-carbethoxypropyl)isocyanurateTris(2-carboxamidoethyl)isocyanurate Tris(2-carboxyethyl)isocyanurateacid chloride Tris(2-carboxyethyl)isocyanurate acetic anhydride.

What is claimed is:

l. A process for the preparation of compounds of the wherein R ishydrogen, methyl 'or ethyl and X is selected from the group consistingof halogen, OR wherein R is hydrogen, alkyl, cycloalkyl, aryl orhalogen-substituted alkyl, and NR -,R wherein R and R are independentlyselected from the group consisting of hydrogen, alkyl or aryl whichcomprises pyrolyzing an isocyanurate compound of the formula:

' alkyl acrylate which comprises pyrolyzing atris(Z-carbalkoxyethyl)isocyanurate.

5'. The process of claim 4 wherein said acrylate is ethyl acrylate andsaid isocyanurate is tris( 2-carbethoxyethyl)isocyanurate.

6. The process of claim 1 for the preparation of an acrylamide whichcomprises pyrolyzing a tris(2-carboxamidoethyl)isocyanurate.

7. The process of claim 1 for the preparation of acryloyl chloride whichcomprises pyrolyzing the acid chloride oftris(2-carboxyethyl)isocyanurate.

8. The process of claim 1 wherein said pyrolysis comprises heating saidisocyanurate at a temperature in excess of about 150 C. for a time inexcess of about 30 minutes.

9. The process of claim 8 wherein the temperature of said pyrolysis iswithin the range of about l-250 C.

10. The process of claim 1 wherein said pyrolysis is conducted atsub-atmospheric pressure.

11. A process for the preparation of acrylic acid and alkyl estersthereof which comprises heating tris(2-carboxyethyl)isocyanurate or atrialkyl ester thereof at a temperature within the range of aboutl70-250 C. for a time in excess of 30 minutes.

2. A process according to claim 1 wherein R1 is hydrogen.
 3. The processof claim 1 for the preparation of acrylic acid which comprisespyrolyzing tris(2-carboxyethyl)isocyanurate.
 4. The process of claim 1for the preparation of an alkyl acrylate which comprises pyrolyzing atris(2-carbalkoxyethyl)isocyanurate.
 5. The process of claim 4 whereinsaid acrylate is ethyl acrylate and said isocyanurate istris(2-carbethoxyethyl)isocyanurate.
 6. The process of claim 1 for thepreparation of an acrylamide which comprises pyrolyzing atris(2-carboxamidoethyl)isocyanurate.
 7. The process of claim 1 for thepreparation of acryloyl chloride which comprises pyrolyzing the acidchloride of tris(2-carboxyethyl)isocyanurate.
 8. The process of claim 1wherein said pyrolysis comprises heating said isocyanurate at atemperature in excess of about 150* C. for a time in excess of about 30minutes.
 9. The process of claim 8 wherein the temperature of saidpyrolysis is within the range of about 170*-250* C.
 10. The process ofclaim 1 wherein said pyrolysis is conducted at sub-atmospheric pressure.11. A process for the preparation of acrylic acid and alkyl estersthereof which comprises heating tris(2-carboxyethyl)isocyanurate or atrialkyl ester thereof at a temperature within the range of about170*-250* C. for a time in excess of 30 minutes.